Nickel-metal hydride batteries, which use a hydrogen-absorbing alloy powder as the negative electrode material, are gaining attention as a power supply for electric cars and the like, since durability (life characteristics and storage characteristics) is high, and further, output characteristics are excellent. In recent years, lithium-ion secondary batteries are also gradually making an entry for such intended use. Accordingly, in terms of emphasizing the advantages of nickel-metal hydride batteries, further improvements in output characteristics and durability are being anticipated.
As the negative electrode material, a hydrogen-absorbing alloy powder having a CaCu5-type (AB5-type) crystal structure is mainly used. However, in terms of improving durability, in the case of MmNi5 (Mm is at least one of rare earth elements) for example, substituting a part of Ni with Co, Mn, Al, Cu and the like is often the case. In addition, in terms of aiming to achieve higher capacity while also improving durability, substituting a part of Site A with a Group 2A element such as Mg, Ca and Sr is being proposed. According to this proposal, the hydrogen absorption amount within a predetermined pressure range (hereinafter referred to as PCT capacity) increases (c.f., Patent Document 1). In addition, preventing elution of Mn and suppressing degradation of discharge characteristics by substituting a part of Site B with Mg are being proposed (c.f., Patent Document 2).    Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-42802    Patent Document 2: Japanese Laid-Open Patent Publication No. 2004-119271